Using Casidiam Coated wrist pins on endurance engines, every once in awhile we will get scratches on the pins. Either on each side where the rod rides, or right in the center. They are so small and minute, they almost seem like it's the coating coming off, but is like a scratch that you can catch with your fingernail. Any thoughts? With same engine specs, this only seems to happen 1 out of Five engines.

I have seen this a couple of times on BBC. From what I observed it seemed that the oil hole in the rod(bushing) had a sharp edge or burr that caused a scratch in the coating that cascaded from there. by the way these were casidium coated titanium pins so once even a small amount of galling started it was over in a hurry. How much pin clearance are you running?

bsfc-With a .868 pin, we are running .0013-.0015 clearance. The rods have no bushing and have the chamfered hole in the top. We sometimes see the scratches in the middle where the oil hole is and also see scratches where the edges of the rod would be. Deep scratches that certainly you can catch your nail on.

Its normal and I have seen no failures caused by small scratches but if you can catch your fingernail on it,,, well,, thats a hard one. If your having galling problems the quickest fix is to open up the clearances. Most engine builders that I have talked to run about .002 to .0025 for a 1.030 diameter pin and .0015 to .002 for a .990 pin. We just started to hone them out to where they would wear too and the galling went away. In other words, if they beat the pin bore out to .0025 then start them out there because that's where they will end up any way! That and DLC, STOPPED our wrist pin problems. If the clearances are to tight the DLC coatings alone will not save you.

The clearances I have mentioned here are for ultra high RPM engines ( 5500-6000 ft/min piston speeds) with dry sump oiling systems. I am sure that moderately high RPM endurance engines ( 4500 to 5000ft/min) would require different clearances. The demons and gremlins are in the high RPM range . We never had a problem on the Pro Truck engines until they went passed 9800 and at 10000rpm they would eat the wrist pins out of the engine instantly. It took a long time to work through it and figure out what fixed it. Casidium ( DLC) and opening up the clearances to .002 on a .990 pin stopped it.

Darin Morgan wrote:Its normal and I have seen no failures caused by small scratches but if you can catch your fingernail on it,,, well,, thats a hard one. If your having galling problems the quickest fix is to open up the clearances. Most engine builders that I have talked to run about .002 to .0025 for a 1.030 diameter pin and .0015 to .002 for a .990 pin. We just started to hone them out to where they would wear too and the galling went away. In other words, if they beat the pin bore out to .0025 then start them out there because that's where they will end up any way! That and DLC, STOPPED our wrist pin problems. If the clearances are to tight the DLC coatings alone will not save you.

The clearances I have mentioned here are for ultra high RPM engines ( 5500-6000 ft/min piston speeds) with dry sump oiling systems. I am sure that moderately high RPM endurance engines ( 4500 to 5000ft/min) would require different clearances. The demons and gremlins are in the high RPM range . We never had a problem on the Pro Truck engines until they went passed 9800 and at 10000rpm they would eat the wrist pins out of the engine instantly. It took a long time to work through it and figure out what fixed it. Casidium ( DLC) and opening up the clearances to .002 on a .990 pin stopped it.

Do you think the inertia load of the piston was ovalizing the pin bore? 10K is well over 5000gs assuming a 3.25-3.3 stroke, and more if the stroke was longer. It probably elastically deformed and returned to round so you wouldn't see much out of round on a teardown.

Thank you for the replies guys. We have found that thinner wall thickness wrist pins tend to flex and oval the pin bores in the pistons. What is the wall thickness of the pins you are using Darren? I would have to think over .170 thick.

Darin Morgan wrote:Its normal and I have seen no failures caused by small scratches but if you can catch your fingernail on it,,, well,, thats a hard one. If your having galling problems the quickest fix is to open up the clearances. Most engine builders that I have talked to run about .002 to .0025 for a 1.030 diameter pin and .0015 to .002 for a .990 pin. We just started to hone them out to where they would wear too and the galling went away. In other words, if they beat the pin bore out to .0025 then start them out there because that's where they will end up any way! That and DLC, STOPPED our wrist pin problems. If the clearances are to tight the DLC coatings alone will not save you.

The clearances I have mentioned here are for ultra high RPM engines ( 5500-6000 ft/min piston speeds) with dry sump oiling systems. I am sure that moderately high RPM endurance engines ( 4500 to 5000ft/min) would require different clearances. The demons and gremlins are in the high RPM range . We never had a problem on the Pro Truck engines until they went passed 9800 and at 10000rpm they would eat the wrist pins out of the engine instantly. It took a long time to work through it and figure out what fixed it. Casidium ( DLC) and opening up the clearances to .002 on a .990 pin stopped it.

Do you think the inertia load of the piston was ovalizing the pin bore? 10K is well over 5000gs assuming a 3.25-3.3 stroke, and more if the stroke was longer. It probably elastically deformed and returned to round so you wouldn't see much out of round on a teardown.